Sea holding in rising material (5)
I believe the answer is:
denim
'material' is the definition.
(denim is a kind of material)
'sea holding in rising' is the wordplay.
'sea' becomes 'med' (abbreviation of Mediterranean).
'holding' means one lot of letters goes inside another.
'rising' says the letters should be written in reverse (going up in a down clue).
'med' going around 'in' is 'mined'.
'mined' back-to-front is 'DENIM'.
(Other definitions for denim that I've seen before include "Mined badly for a hard-wearing fabric" , "Tough cotton fabric" , "Durable material" , "Coloured cotton twill" , "Hard-wearing cloth" .)